Liquid level control mechanism



Sqn. 1s, 1951 W. M. MERCER LIQUID LEVEL CONTROL MECHANISM Filed March l0, 1947 @yf-f QUID Ourujr s j; 37 644? J 4a 44,

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LIQUID LEVEL CONTROL MECHANISM Filed March 10, 1947 y 2 Sheets-Sheet 2 y 53 ,39ww

IN V EN TOR.

naz/0mg Patented Sept. 18, 1951 UNITED STATES PATENT OFFICE 3 Claims. (Cl. 137-68) My invention relates to liquid level controls,

and has particular reference to a level responsive pilot valve adapted to actuate a control valve or other power driven mechanism that directly corrects the liquid level.

My invention may be advantageously utilized for automatically controlling and maintaining a constant liquid level in a pressure container by controlling the incoming or outgoing liquids, or both. Such controls are particularly desirable in distillation units wherein fractional distillation is utilized to separate the components of a complex liquid mixture. Such distillation units often comprise a chamber or pressure vessel in which may be placed a large number of heating tubes Which may be heated in any suitable fashion, for example by constant temperature steam. lf the vessel is completely filled with liquid a maximum heat absorption takes place, resulting in a maximum rate of evaporation. If this maximum rate of evaporation is excessive, there is an excessive bubbling or boiling of the liquid mixture that carries off the heavier components along with the lighter components. On the other hand, if the liquid level becomes too low within the pressure vessel, the rate of evaporation will be so low that the lighter components will remain and will be drawn ofi" along with the heavier components of the mixture.

Apparatus of the type just mentioned is used, for example, in separating the components of natural gas gasoline. Such gasoline may be made up of various components such as propane, isobutane, normal butane, isopentane, pentane, etc. A separation of these components by fractional distillation is accomplished by pumping the liquid into a propane distillation unit, otherwise known as a depropanizer unit. This depropanizer unit is used to distill olf or separate the propane from the other components, and accordingly may be operated at about 300 p. s. i. so that the resultant propane gas will be under a sufficient pressure so that it may be economically condensed into liquid propanes. Normally the distillation may take place in specific distillation units when the pressure vessel is one-third full, and if the level becomes higher than that precisely predetermined, there will be an excessive boiling off of the heavier components, and if the liquid level becomes too low, the propane will not be effectively removed and will remain in the mixture and will be carried over to subsequent distillation units.

Such distillation units at present employ a float responsive control mechanism for maintaining the liquid level. This level may be maintained either by regulation of the incoming mixture, or by regulation of the out-flow of the depropanizer liquid. Such control mechanisms at present generally include a shaft rotating connection between the float and the control mechanism, and the shaft passes out through the pressure vessel through a packing gland sufficiently strong and tight to seal the operatingpressure. With this type of liquid level control it requires a great amount of variation in the liquid level to operate the control due to the friction encountered at the packing gland. For example, variations of four inches are often required to operate this type of control mechanism, whereas for economical operation the liquid level should not vary more than a half inch.

My invention provides an apparatus that is inherently free from frictional effects, inasmuch as packing glands are completely eliminated. The movement of a oat in response to a change of liquid level operates a finely adjusted valve mechanism which in turn may operate a pilot valve controlling flow to a power operated valve. The control achieved by apparatus embodying my invention accordingly may be held within the desired tolerances of a half inch or le-ss.

It is therefore an object of my invention to provide a liquid control mechanism that is entirely free fromv packing glands.

Another object of my invention is to provide a liquid control mechanism that is entirely free from sliding or rotational engagements such as would require bushings or bearings with their resultant frictional drag upon the apparatus.

A further object of my invention is to provide a pressure responsive pilot valve mechanism for operating a power device that directly controls a liquid level.

Still another object of my invention is to provide a pilot valve actuated by a iioat responsive valve.

A further object of my invention is to provide a power Valve control system wherein a pilot valve may utilize a slow bleed from a high pressure source of operating fluid.

Other objects and advantages of my invention will be apparent in the following description and claims, considered together with the accompanying drawings, in which Fig. lis an elevation view partly in section and partly schematic of a distillation unit employing a control mechanism and system embodying principles of my invention;

Fig. 2 is an enlarged sectional view taken along the line II-II of Fig. 1 illustrating the assembly of the multiple bellows actuator; and

Fig. 3 is a sectional view taken along the line III-III of Fig. 1.

Referring to the drawings, a distillation unit 5 may include a plurality of heater tubes 6 fed by a common header I which may be connected to any suitable heated fluid such as constant temperaturesteam. Liquid may be fed into the distillation unit 5' by any suitable means such as a constant feed pump or fixed orifice so as to form a pool of liquid 8, the level of which must be precisely controlled so that only a xed number of heating tubes 6 are immersed therein. The number of tubes thus immersed may be determined experimentally or by calculation so as to obtain a xed rate of evaporation that willA remove only the desired component fromthe liquid. For example, if the liquid 8 were natural gas gasoline andv it was desired to removeonly the propane, the liquid level might'be that indicated in Fig. l, which level mayV also be identified by the numeral 9`. The pressure vesselv 5 might be maintained at any. suitable pressure without affecting in any respect the operation of the illustrated mechanism embodying the invention, and for example might bemaintained at 300 p. s. i.

' The distillation of a light component from the liquid 8 will resultV in a heavy remaining liquid that must be. periodically drained oi to maintain the liquidV level as the heavier portions of the incoming liquid accumulate. Accordingly an outlet conduit II may be provided in which a suitable hand shut-off valve I2 may berinserted. and the ilow through the conduitv II may be further controlledby a power operated valve I3. furnished particularly in accordance with the invention.

In the normal operation of the. mechanism,'the

hand valve l2 is completely openedand thepower A operated valve I3 alone controls the outletow. The power operated` valve I3 may be` operated in any suitable manner, either mechanically, elec,-

trically, or hydraulically, but I prefer for the .Y

illustrated embodiment to employ compressed air as the operating power medium. Accordingly a diaphragm assembly I 4` may be secured to the top of the valve I3. and a piston rod actuator I5 :may be secured thereto to actuate the, valve I3.

Air under pressure may be supplied from any suitable source, such as a compressor, and may pass through a. lter unit I6, ableeder orifice or throttle I'I, through a'tube I8, into a pilot valve housing IS provided particularly in accordance with the invention. The throttled'air may then pass into a flexible bellows` 2I which may be in communication with aV conduit 22A leading directly to thev diaphragm actuator I4 for thevalve I3.

While various level responsive mechanisms could be employed, I prefer at. presentto use a float as my liquid level responsive mechanism, and accordingly IY provide.. af iloat housing 23 which, may be connected on either end by conduits 24fcoupled to the pressure vessel. 5,above and below the desiredV liquid. level line so that a corresponding liquid level Willbe ,maintanedin the float housing. A float 25, may be disposed withinthe housing 23 and may have any suitable construction, for example ofhollow non-corrosive A pressure responsive mechanism may be proe vided within the valve housing 26 by positioning a bellows 29 therein which may be held in place in any suitable manner, for example by an apertured disk 3| to which it may be secured, which disk may be sealed against a stepy in the bore 2l' and held in place by a snap ring 32. The left end of the bore 2l may be completely sealed by meansv of a solid disk 3.3 sealed on another step of the bore 2Tv and held in place by a snap ring 34. The middle portion of the bore 2I may be vented to atmosphere by means of a slot 35 in the top of the main body 26, which slot may be disposedY opposite arslot 36 in the pilot valve body L9., A ventx3I may be provided in the pilot valve body I9 to directly communicate the interior of that valve body. toy atmosphere.

Inasmuch as variations in the pressure in the distillation unit 5 may upset the precise control desired, I provide a counterbalancing bellows 33 Y secured in any suitable fashion within the bore 2'1, for example by anl apertured disk 39sealed against a shoulder andA held in place bya snap ring 4I. The right end of the bore 2'? may'be completely sealed by a solid disk l2-positionedand sealed Vagainst a shoulder by means of a snap ring 43. As previously mentioned, thefright endl of the bore Z'I is communicated to the'interior of thefloat housing 23 by means of the' passage 23, and accordingly the pressure within the distillation unit 5 will be transmitted through the tubes disposed within the pilot` valve housing I9v may' have a fitting 44 on the inner end thereof into which may be threaded a valve seat member l5- through which may project a pcppet valve 46 to seat on the interior of the bellows ZI. The pilot valve 45 may have-aV stem'I secured thereto engageable by means of an adjustable stem 48 threaded into an actuator member Shaving its lower end disposed between, and securely fastened to, the adjacentends of the bellows 2i)Y and- 38. As previously noted, a power supply medium may be compressed air under pressure which is bled by the throttle Valve I`I into theexpansible bellows 2|. Accordingly, as the pressure within the bellows 2l builds up, the bellows will-elastically expand, and if the poppet valve it ismaintained in a stationary-position, the valve seatl5 will move away from the poppet 4S, permitting this air to escape-through the fitting lla-to the interior of the'housing I9 and thence to atmosphere through theventl'. If, however, itA is-desired to buildup a suflicient pressure'within the bellows 2 IY so asto cause the diaphragm actuator of the outlet valve I 3 tooperate, thecontrol mechanism for-the pilot poppet 46 may cause this poppet to move to the right along with the expanding'bellows, thus sealing `within the bellows 2| the air bled from the throttle Il. In this fashion the pressure within the bellows 2i may be built upf to any desired pressure short of; the maximum available pressure so that an actuating pressure may be applied to the diaphragm unit I4. Y

From the foregoing operation of the pilot valve, and assuming that the outlet valve Isis normally closed, it will be realized that a movement of. theV actuator member IIS!A t'o the-'right willV be desired when the liquid level becomes toohigh. This will cause the pressure to develop within the pilot .bellows 2I so that the pressure may be applied to the Valve actuator I4. If, however, the liquid level becomes too low, it is necessary to move the actuating member 49 to the left so as to open the valve 45 and thereby bleed the pilot bellowsl into atmosphere, removing any actuating pressure from the diaphragm assembly I4. This movement of the actuating member 49 may be effected in accordance with my invention by utilizing the pressure within the oat housing 23, which of course'will be the same as the pressure within the distillation unit 5. Accordingly the main valve body 26 may be apertured above the iioat housing 23 as at 5I, and a valve fitting 52 may be threaded into the lower end thereof and sealed against the surface of the valve body 25 that is exposed to the float housing pressure. A smaller bore 53 may be concentrically extended from the inner end of the bore 5I, and a cross bore 54 may intersect with this smaller bore 5S. A cross bore 55 may communicate the larger bore 5I to the left end of the main bore 2'I by means of a p-arallel bore 55. It will be noted that the intersection of the extended bore 53 with the large bore 5I will provide a valve seat 51 so that two aligned valve seats are present; namely the valve seat 51 and a valve seat 58 formed in the fitting 52.

The cross bore 54 may be vented to a low pressure such as atmospheric pressure, but inasmuch as the gas that may escape through this vent will be the gas within the distillation unit 5 that will have commercial value, a conduit 59 may be connected thereto to lead this vented gas to any suitable drain. Y The ow from the interior of the float housing 23 through the valve seat 58 to the pressure responsive bellows 29 and also the ow through the valve seat 51 may be controlled by a doubleended, double-conical pressure supply valve member 6I connected by a thin stem 62 to a pin 63 threaded into the top of the float 25. Accordingly when the oat is raised, the top end of the valve member 6I will seat on the valve seat 5l, closing flow through that valve seat, and at the same time an opening will be present at the valve seat 58 between the valve seat and the thin stem 52. Conversely, if the iioat drops, the lower end of the valve element 6I will seat on the valve seat 53 and the upper valve seat opening 5'! will be open. Accordingly when the liquid level drops, the high pressure gas within the ilo-at housing 23 will be sealed at the valve seat 58 and the pressure responsive bellows 29 will be vented to atmosphere through the conduits 56 and 55, the valve seat 58 and the conduit 54 to the drain line 59. This will cause the bellows 29 to contract due to the superior pressure in the bellows 38, moving the actuating member 49 to the left and unseating the poppet 46 which will allow pressure within the pilot bellows 2| to bleed to atmospheric pressure. The valve I3 accordingly will be closed and no liquid will iiow out of the outlet conduit II. When the liquid level becomes high, the valve seat 5l is closed, and pressure from the interior of the housing 23 ows through the ttings 52 through the passages 55 and 56 to the interior of the bellows 29. gether with the compression of a spring 54 disposed about the valve stem 4l', will urge the pilot 45 to the right, causing the pressure within the pilot bellows 2l to accumulate until an actuating pressure is achieved. A cap 65 may be removed This pressure, to-

from the pilot housing I9 to permit adjustment of the stem 48 and correspondingly adjusting the operating position of the pilot puppet 46.

In operation, the mechanism illustrated will maintain the liquid level control between limits determined solely by the amount of movement oi the pressure supply valve member 6I necessary to uncover one valve and close another. While this control has been achieved within a limit of a half inch in order to meet specic specifications, it will be readily apparent to those skilled in the art that the valve member 6I could be so shaped as to actuate with a much shorter movement or much greater movement, as desired.

The complete operation of the apparatus embodying the invention may best be described with reference to Fig. 1, where it is shown as applied to a distillation unit, as previously mentioned. Assuming that the liquid level 9 is to b-e maintained by controlling the liquid outlet flow through the conduit II by means of the automatic power operated valve I 3, this liquid level will be reected directly in the liquid level within the iioat housing 23 because of the communications with the distillation unit 5 through the conduits 24. When the exact liquid level is maintained, the float 25 will position the double-ended valve member 5I midway between the two valve seats 58 and 5l so that they are both open and there will be a bleed of gas from the interior of the float housing 25 through the valve seats 55 and 5l and through the passage 54 to the drain line 59, where the gas may be recovered or exhausted, as desired. If, however, the liquid level 9 should rise above this normal level as shown, the oat 25 will rise, carrying with it the valve member 6I, closing the valve seat 51, and opening communication wide through the valve seat 53. Thus the full head of pressure within the housing 23, which may be of the order of several hundred p. s. i., will be available for actuation purposes, and this pressure will be transmitted through the passages 55 and 56 to the interior of the pressure responsive bellows 29, which bellows is counterbalanced by the bellows 38 communicated to the oat housing 23 by the passage Z3 shown in broken outline. The pressure on the interior of the pressure responsive bellows 29, together with the spring 4'I within the pilot housing I9, and together with the algebraic sum of various spring loads inherent in the bellows 29, 38, and 2l, will cause the actuating member 49 to move to the right. This will cause the poppet 45 to seat upon the seat 45 so that the slow bleed of air from a high pressure source (not shown) and received through the conduit I8 will build up in pressure within the bellows 2l. When this pressure reaches a required amount it will be transmitted through the conduit 22 to the diaphragm actuator I4, which will cause the valve I 3 to open, causing liquid to be bled out the outlet conduit II, causing the liquid level 9 to drop. This dropping liquid level will be reflected in the liquid level within the float housing 23 and will cause the iioat to drop, unseating the member 6I at the valve seat 6'1 and permitting the pressure to vent to the drain line 59, This will release the pressure within the actuating bellows 29, and the superior pressure within the bellows 38 will cause the actuator 49 to move to the left. This will unseatthe pilot poppet 46, permitting the pressure within the pilot bellows 2I to vent to atmosphere. This will release the actuating pressure within the diaphragm actuator I4, allowing the valve I3 to close. If the liquid level becomesslower` than, normal,..the valve element. 6 if. willseat: completely 'onthevalvezv seat 5 B; l open? ing the communication. through; the valve. seatI 511 wide totheidrain` line 59:v

Itwill; be realized.' thatlthe most accurate control` of.. the liquid level .will be obtained--W-henthe valve lS-is of the variable type So thatit maybe opened to anydesired amount instead-of wide open or fullshut'. Accordingly, therefore, it will be realizedithat the apparatusfjustl described lends itself.` to this Vtype of` controlso that the pressures withinr the pilotbellows 2?!y may vary'from atmospheric to.- the full. available pressure. Accordvingly; therefore, thisrange of pressures-withinthe bellows 2l: may be obtained bythe various positionsof the valve member 6l between its two valvezseats -and. 5l'.Y rilhus-the' mechanism may be continuouslyoperating instead'of being either operating orv non-operating; intermittently. In this manner precise liquid Alevel control may be obtained even within the limit ofmovement` of theyalVemember'Sl that is necessary to close one valve and -,then'the other.

While Il have described my invention with re Yspect to a specific embodiment thereof', I do not limit myself to this specic embodimentV inasmuch as itis obvious to those skilled intheiart that variousmodications may be made-therein without` departing'from the true spirit and scope ciA the invention. Alsoit is obvious that the invention couldl be` utilized-to controlinlet flow as wellf as outlet flow. Accordingly, for these and other reasons, I do not limitrmyself to the specic structure, nor limit myselfl in any Vother Way, except by the terms of the following claims.

l'. A pilot. assembly for regulating the levelof a liquid in a pressure vessel comprising afloat housing communicated with thepressure vessel and open at the top, a oatdisposed within the float housing, a poppetl valvebody disposed upon the housingand sealing thetop,'afpressure responsive bellows disposed within the housing, a com'- munication from the oat housing to the interior of the pressure respons-ive bellows, a counteracting bellows dispcsedwithin'the valve body subject at all times-to the pressure `within thefloat housing; avent connected to thecommunication, a double ended poppet carried by the float projectingginto the communication to seal oi the'vent when Vthe orat moves upwardly and simultaneously to open the communicationA and to close oi the communication when the float moves downwardly and to simultaneously open the vent, aconduitconnected to the Apressure Vessel, a valve for controlling flow in the conduit, a fluid pressure'actuator for actuating the valve, a` source of fluid under-the'pressure having a limitedfluid supply, anexpansible pilot bellows communicated with the'source and thea'ctuator and carry-ing'a valve seat on its mov-- able'end, a valve poppet associated with-the expansible pilot bellows and movable inwardly from the seat to open the valve, and'amechanical connection between the pressure responsivebellows and the pilot poppet, whereby thepoppet will be'- come unseated when the pilot bellows expands past a variable point determinedfby the expansion ofthe pressure responsive bellows.l

2. A pilot assembly for regulating thev level of a liquid in a pressure vessel comprising a float housing communicated: with` the pressure.. vessel and open at the top, a oat disposedwithin'the oat housing, a poppet valve body disposed upon l 8i the housing. andzsealin the: top, apre'ssurefre# sponsive bellows disposed withinfthe housing, a communication: fromfthe .float housing to theV interior of .'the1pressure `responsive bellows', acounf teracting` bellows disposed. within: the .valve body,

subject at alli times to the .pressure within theV Yiioat housing', a ventconnected to the communicaition, a; double ended poppetcarried by the: float projecting into thecommunication to seal off the vent when the float moves upwardly and simultaneously 11o-open the communication and t-o-close oil` the communication when the float moves downwardlyand'to simultaneously open thevent, a conduit' connected tothe pressure-vessel, a Valve for controlling flow. in the conduit, a fluid pres-V sure actuatoriforactuating the valve, arsource of. iiuid under the pressure havinga.V limited fluidv supply.,v an expansible bellows-communicated withl the source and-the actuatorand carrying a= valve seat-on its movable-end, a Valve member associ-V atedwitli the'expansible pilot bellows and mov-- able inwardly from the seatto open the valve, a mechanical connection between the pressure responsivev bellows and the pilot valve member, whereby the pilot valve member will become unseated when the pilot bellows` expands past a variable point'determined by the expansion ofthe pressure `responsive bellows, and an adjustment disposed between the mechanical-connection and the pilot valve member. Y

3. 1n a liquid levelV controller for vessels` in which aliquid is partially evaporatedandV having amain valve for controlling the-rate of flow of liquidl therethrough actuated by pneumatic power controlled by a pilot Valve,` the combination of a iloat exposed to the liquid in thev vessel to assume a position corresponding tothe level of the liquid in the vessel,` a valve chamber having a pair of opposed Valve seats, oneicommunieating Ywith the gas above the liquid level in the vessel and the other communicating with a vent, a valve member actl'iatedby.y the float between closing positions onl each of said seats,` respective- 1y; to'control the-now of gas through said vent inv accordance with thev position of said float and a pilot valve4` actuator for'movementy relative to said pilot valve, means exposing one side'of said actuator-continuously to the pressure of` gas in said vesselto urge'the'actuator in one direction,v andl means exposing the' opposite side of said actuator Vtosaicl vent toapply pressure thereto in' accordanc'ewithithe. position ofA said valve member.'

W1LLIAM`M. MERCER.

REFERENCES' CITED The. Yfollowing references are of record in the fileof. this patent.: 

